Wednesday, July 01, 2009

One of these days I'm going to tour all the underground lairs dedicated to strange and wonderful research, from the the famed LHC tunnel to the lesser-known New Mexican salt mine where scientists at the Enriched Xenon Observatory hunt for the most exotic of particle decays. Now I've got one more stop to add to my subterranean science world tour: the Sanford Laboratory.

Dedicated last Monday, it's hard to believe, from looking at the pictures of the cheerful attendees in hard hats hanging out in a tunnel of bare rock, that this will one day be home to a high-tech physics lab that will be in a unique position to tell us some very interesting stuff about the nature of the universe. As recently as early May, before the pumping was finished, this cavern of the former Homestake gold mine had been filled with water from the mine's closing in 2002. I'm jealous of the attendees, who descended via mining elevator to the site, 4850 feet, or the better part of a mile, below the surface. Former miners even participated in the dedication ceremony by mounting a plaque on the rocky wall—always the first step in starting any successful scientific endeavor.

The Sanford Lab will be home to at least two experiments studying some very strange stuff indeed, and you've got to love their names. The Large Underground Xenon detector, or LUX, will search for dark matter particles, while the Majorana (named after a defunct Mayan deity, perhaps?) will look for something called "neutrinoless double beta decay."

Let's start with Majorana, because it’s a cousin of the aforementioned Enriched Xenon Observatory, or EXO, which is also deep underground. Believe it or not, "neutrinoless double beta decay" does really mean something, if we parse it in physics-speak via this great explanation from Symmetry magazine:

...this means watching for an isotope of xenon decaying into barium, giving off two electrons (the double beta decay), but without giving out any neutrinos. A beta decay process gives off one neutrino, so how could this even be possible? It only works if the neutrino is its own antiparticle, so that the two beta decays each have a neutrino which essentially cancel each other out, like matter and antimatter annihilating. And the possibility that process exists is the reason for the experiment.

If neutrinoless double beta decay is observed, it means the neutrino must be its own antiparticle, a key unknown in the study of neutrinos. If the neutrino is indeed its own antiparticle, it has all kinds of implications for the structure of the Standard Model and the relationships between the fundamental particles.

Particles that are their own antiparticles are termed "majorana" particles, after the physicist Ettore Majorana who thought them up. And you thought that scientists just like to name their experiments weird things for the heck of it.

So why do we have to do this underground? It all comes back to neutrinos, one of the most elusive beasts in the fundamental particle menagerie. That's why it is wearing this adorable bandit mask:

Trillions of neutrinos from the sun are passing through your body every second. But because they have no charge and almost no mass (electrons are hulking monsters in comparison), they fly through just about anything, including your head, without leaving a trace. Gravity barely acts on them; they interact most strongly with matter via the weak force.

So imagine you're sitting at the edge of a very still pool. You want to watch the ripples that are caused by a single drop of water falling into the water. But imagine now that it's raining. Pouring, actually. The water's suddenly alive with ripples and dimples and tiny waves. So how are you supposed to see just one ripple in a thousand?

Detecting neutrinoless double beta decay is so difficult that it makes this task look like a piece of cake. So of course, you need an experiment that's like a still pool, protected from the constant shower of cosmic rays, high-energy particles from distant supernova that bombard the earth. In addition to the 4,850 feet of solid earth, ultra-pure experimental materials and extensive shielding will protect Majorana from excess noise. The other experiment at Sanford Lab, LUX, will also benefit from a batcave-like location. LUX will be looking for WIMPs, or Weakly Interacting Massive Particles, which scientists think make up dark matter. Dark matter, besides making a little shiver run down my spine, accounts for about 5/6 of the universe's matter, but doesn't act electromagnetically, meaning we can't see it with telescopes, whether they see in radio waves, infrared, or gamma rays. (And we really don't know what it is, unless you count what a physicist once told me: "Dark matter is what keeps me up at night, what nibbles away at my soul." I love it when physicists wax poetic.) It's also the missing piece that makes the whole puzzle of the universe fall neatly into place along the lines Einstein drew. So if regular old matter is made up of protons and neutrons, scientists think dark matter could be made up of (soul nibbling) WIMPS.

So until I get a grant to write my "tour of the world's physics bat caves" travel guide, I'll have to content myself with amazingly creepy images like the following, of the proposed Deep Underground Science and Engineering Laboratory, of which Sanford Lab will be a part. A smorgasbord of particle and nuclear physics, geology, hydrology, geo-engineering, biology, and biochemistry, DUSEL will have a "Deep Campus" at a whopping 8,000 feet below ground.

4 comments:

In grad school I worked for a year on MINOS, the nutrino project out of Fermilab. I got to do some work underground at Fermilab and was able to tour the labs of the Soudan mine in northern MN. So cool!

Way to go anonymous 3, defeatism is the key. Have you thought about entropy? Maybe parameters are too small for detection; coupled with the amount of matter(dark) exceeds its larger peers,by volume. ie. cosmic microwave background....history of the big bang.